Musicians know something about brains. They know if they repeat something a whack of times, then go away, then try again, at some point the thing works on its own. Some people say muscle memory. I find that a wee banal because this is so much more mystical than that. I prefer to say magic, because magically the hands (or fingers or feet) can do that thing it couldn’t do when you first tried.
And you imagine it a lot, especially while you are trying to reach that place you have not yet reached. Almost there… part of the way…. more and more each time….. and you keep repeating the effort, try again, let’s try again, slower, faster, in a different chair, after a break yada yada – the brain knows you want to do this. Even when you are away from the instrument you still run through the desire to master this thing you haven not yet mastered.
So I’m thinking, if that happens (and it does) then perhaps worrying about whatever horrible thing one might worry about (ill health, rejection etc.) constantly, is a way of replaying to the brain a certain picture, albeit undesirable, but we’re imagining it over and over just as we do when practicing. Like maybe that isn’t so wise.